Conduction heating of formations



Jan. 21, 1969 J, WARREN CONDUCTION HEATING OF FORMATIONS Filed Oct. 5,1966 lldldllfilili with nlhlli;

..).0 I l I I N VE N TOR. JQSEPH E. MRRL-N United States Patent3,422,893 'CONDUCTION HEATING 0F FORMATIONS Joseph E. Warren,Pittsburgh, Pa, assiguor to Gulf Research & Development Company,Pittsburgh, Pa., a corporation of Delaware Filed Oct. 3, 1966, Ser. No.583,887 US. Cl. 166-40 Int. Cl. EZlb 43/24; E21b 43/26 5 Claims ABSTRACTOF THE DISCLOSURE This invention relates to a method of producingviscous hydrocarbon fluids from a hydrocarbon-containing formation whichis adjacent an impermeable formation.

A considerable number of reservoirs presently being produced in theUnited States are characterized as containing viscous crude. Whenreservoirs are found to possess heavy viscous fluids the operator isfaced with the problem of choosing a well stimulation means which willyield high ultimate recoveries without subjecting the well to adverseconditions.

One method of producing oil from formations containing heavy viscouscrudes is to initiate in situ combustion Within thehydrocarbon-containing formation to heat the in-place oil and therebyincrease its fluidity. This method requires careful control by theoperator, utilizes expensive equipment and consumes a considerableamount of the .in-place oil. In situ combustion also produces largeamounts of heat and high temperatures which coke part of the oil in theformation. The presence of coke in the formation will lower theproductivity of the well. Coking of the oil will also utilize a portionof the reservoir oil and make it unavailable for recovery.

Another method of heating subterranean formations to increase thefluidity of in-place viscous crudes is to burn injected gases withinformations adjacent the reservoir or within the hydrocarbon-containingreservoir itself. These methods likewise have disadvantages owing to thehigh temperatures created, the amount of supervision required and theformation of coke which will lower the efficiency of the operation.

In certain areas a permeable sand is separated from the viscoushydrocarbon-containing formation by a thin impermeable stratum such asshale. Attempts have been made in the past to heat these upper or lowersands and thereby heat the remote hydrocarbon-containing forma tions byconduction. Such attempts are ineflicient because of the heat lossessuffered in conducting the heat through two reservoir stratums. Fluidscontained in the heated adjacent permeable stratum will also absorblarge amounts of the heat thereby further decreasing the efliciency ofheating the hydrocarbon-containing stratum.

This invention resides in an improved method for thermally stimulatingproduction of viscous oils utilizing a single well. Steam is injecteddown the well and outwardly from the well through a fracture in animpermeable formation adjacent the formation containing the viscous oilto be produced. Flow of steam into the oilbearing formation is blocked.Injection of steam into the 3,422,893 Patented Jan. 21, 1969 fracture iscontinued until the desired heating of the viscous oil by conductionfrom the fracture through the intervening impermeable formation isaccomplished. The fracture is then isolated from the Well bore, theoil-bearing formation is placed in communication with the well bore, andthe pressure in the well bore is reduced to cause flow of oil into thewell.

Injection of the steam through the impermeable formation is accomplishedby creating a fracture through this stratum by pumping a fluid down thewell bore and into the impermeable stratum at a rate which will producea pressure greater than the overburden pressure on the formation. Owingto the impermeable properties of the stratum there will be nocontamination or commingling within the hydrocarbon-containingformation. The utilization of steam for the heating medium of thisinvention will allow greater temperature control and will enable theoperator to supply large quantities of heat to the adjacenthydrocarbon-containing formation while injecting only a small volume ofheating medium into the well. Obtaining high heat delivery from lowvolumes of heating medium is a necessity of this invention owing to thelimited space provided for the heating medium.

In the drawing:

The drawing is a diagrammatic view partially in section representing awell bore and the equipment used for the operation of this invention.

In the drawing, numeral 2 indicates a well bore in which casing 4 hasbeen installed with cement 6 placed in the annulus between the well bore2 and the casing 4. Tubing 8 extends from the surface and is setopposite the hydrocarbon-containing formation 14. A straddle packer 10is run on the tubing and set in a position to isolate perforations 18opposite a fracture 16, as preferred in this invention, created throughan impermeable stratum 12. Other perforations 18, located below thestraddle packer 10, provide a path for the fluid to flow from thehydrocarbon-containing formation 14 into the well.

In the operation of this invention, as indicated in the drawing, thestraddle packers are set in an open position which permits steam to bedelivered down the tubing and into the fracture. Thehydrocarbon-containing formation below the packers is sealed by thevalve arrangement of the straddle packers. Steam is delivered down thetubing and into the fracture which extends through the impermeablestratum. Injection of the steam will continue until the portion of thefracture desired to be treated is heated to at least 400 F. for adesired duration. Injection .is terminated and the tubing, as preferredin this invention, is rotated to seal the interval between the straddlepackers and open the tubing to communicate with the lower zone. Thepressure inside the well bore is then lowered and fluid entering thewell bore below the straddle packers is produced.

Injecting steam through the impermeable formation will heat to hightemperatures the adjacent hydrocarboncontaining formation. Owing to thelimited space provided for the heating medium, steam or steam withrelatively small amounts of gas is the injection fluid that must beutilized for this invention. The use of steam or steam and gas mixturesas the heating medium of this invention will permit sufficient heat tobe delivered to the adjacent formation while injecting only a smallvolume of heating fluid into the Well.

Owing to the dense impermeable properties of the fracture zone, thecondensed liquids from the injected steam cannot escape into thehydrocarbon-containing formation. It will therefore be possible to heatthe hydrocarboncontaining formation without commingling the injectingfluids with the formation oil.

Most impermeable strata, such as shale, have parallel bedding planes. Afracture may therefore be created through thin sections of this stratumwithout breaking the fluid seal formed by these impermeable layersbetween adjacent formations and the hydrocarbon-containing formation.

In the injection of steam of this invention, the impermeable formationfracture may be initiated or ext-ended by injecting the steam at a ratewhich will produce a pressure exceeding the overburden pressure on theformation. This will not produce detrimental effects because these shaleformations will fracture along their bedding planes and not .into anupper or lower formation. A greater radial treatment depth may thus beaccomplished by extending the fracture to distances more remote from thewell bore.

Owing to the injection pressures that may be generated during injectionof the steam, the fracture does not need to be propped in an openposition in order to perform subsequent heating treatments. It alsofollows that the initial fracture through the formation may be createdby the injection of this steam.

In this invention it is preferred that injection of steam shouldcontinue until the fracture is heated to a temperature in the range of400 F. to 700 F. The duration of this treatment is a variable dependentupon the radial extent to which the operator desires to heat thehydrocarbon-containing formation and the thickness of this oil-bearingformation. In formation conditions wherein the pay zone is thin it maybe advisable for the operator to inject into the impermeable formationover long periods of time. However, in thick pay formations, it may beadvantageous to extend the heat to relatively short radial distancesfrom the Well bore, preferably 100 to 150 feet, cease injection andproduce through the same Well. As the formation cools and productiondiminishes the fracture may again be heated. It is recommended howeverthat in each subsequent reheating the radial distance heated to above400 F. should be extended.

Owing to the ease of operation and equipment involved, it is animportant advantage of this invention to use steam as the heattransferring material. The utilization of steam permits the operator toeffectively heat the reservoir with out subjecting the oil-bearing sandsto the excessive temperatures that may be produced by in situ heatingmethods. Steam heating techniques will also allow the operator to supplylarge amounts of heat while injecting only a small volume of fluid intothe impermeable stratum because of the larger amount of heat that isdelivered to the adjacent formation as the steam condenses into Water.

It has been found that a more advantageous and more efficient heatingoperation is conducted if small amounts of a gas, such as natural gas orair, is mixed with the steam. Where such a mixture is injected into theimpermeable strata the partial vapor pressure of the steam can be lowerthereby keeping the mixture in a vapor state for longer intervals oftime as injection continues. This allows the hot injected fluid to beextended to greater radial distances from the well bore beforecondensation occurs with its resultant rapid heat release.

Heating 2. hydrocarbon-containing formation by this method can therebybe efliciently accomplished under controlled temperature conditionswithout subjecting the inplace reservoir fluids to contamination orwaste.

The use of steam as the heating medium allows the operator to deliverlarge amounts of heat to the adjacent formation while injecting only asmall volume of heating material into the limited space provided.

I claim:

1. An intermittent producing method for recovery of oil through a singlewell penetrating a subterranean oilbearing formation and an adjacentimpermeable formation, the impermeable formation having a fracturetherein spaced from the oil-bearing formation and extending outwardlyfrom the well, comprising isolating the oilbearing formation from theupper part of the well, injecting steam into the well and displacing thesteam down the well and into the fracture, continuing injection of thesteam until the portion of the fracture desired to be heated is heatedfor a desired duration, terminating injection of the steam into thewell, isolating the fracture from the upper part of the well and placingthe oil-bearing formation in communication with the upper part of thewell, lowering the pressure inside the well, and producing fluids whichenter the well.

2. A method as set forth in claim 1 in which the fracture is heated to atemperature in the range of 400 F. to 700 F.

3. A method as set forth in claim 1 in which the fracture is heated toat least 400 F. for a distance of to feet from the well bore.

4. A method as set forth in claim 1 in which the injected fluid is amixture of a permanent gas and steam.

5. A single well method of producing hydrocarbons from a subterraneanhydrocarbon-containing formation adjacent an impermeable formation, saidformations penetrated by a well bore extending downward from the surfaceof the earth comprising isolating the hydrocarboncontaining formationfrom the upper part of the well, injecting steam down the well bore andinto contact with the impermeable formation, increasing the pressure onthe steam in contact with the formation to create a fracture through theimpermeable formation with the steam, continuing injection of the steamuntil the portion of the fracture desired to be treated is heated to atleast 400 F. for a desired duration, terminating injection of the steam,isolating the fracture from the upper part of the well bore and placingthe oil-bearing formation in communication with the upper part of thewell bore, lowering the pressure inside the well bore and producingfluids which enter the well bore.

References Cited UNITED STATES PATENTS 2,813,583 11/1957 Marx et al.166-40 X 3,155,160 11/1964 Craig et al. 16640 3,167,120 1/1965 Pryor166-10 3,180,413 4/1965 Willman 16640 X 3,284,281 11/1966 Thomas 16611 X3,330,353 7/1967 Flohr 1662 X 3,346,048 10/1967 Strange et al. 16642 XSTEPHEN J. NOVOSAD, Primal) Examiner.

US. Cl. X.R. 16642

